If I understand correctly, 便利さ and 利便性 have the same meaning.
Is there any difference in nuance or usage?
Maybe 利便性 is more formal?
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Sign up to join this community便利 is a quality something provide, 利便 is a quality people perceive.
○ 便利を図る
○ 利便を図る○ 便利な製品
? 利便な製品? 人々の便利さ
○ 人々の利便性
It's true that 利便性 sounds more formal than 便利さ, but it mainly comes from the difference between -性 and -さ. Theoretically, 便利 also has a form of 便利性 as well as 利便 has 利便さ, but apparently disfavored than their counterparts according to Google search.
Yes, "利便性" is more formal.
"[利便性]{りべんせい}" = "便利さの[程度]{ていど}"
example(nuance)
"便利さが[高い]{たかい}" > bad.
"便利さの程度が高い" > not wrong. not too bad.
"利便性が高い" > right. good.
便利(な) can modify almost anything; 調理器具, 文房具, ソフトウェア, (何でも売っている)店, (何でも答えてくれる)ウェブサイト, (色々な状況で使える)ことわざ, (頼みを断らない)友人, etc. (Don't use the last example unless you want to lose your friends.) Commodities such as 鉛筆 or 包丁 are almost exclusively modified by 便利.
利便性の高い tends to modify larger and/or public things, mainly focusing on their accessibility rather than functionality. For example, (駅から徒歩で1分の)家, (24時間営業の)店, (大都市を短時間で結ぶ)路線, (簡単な手続きで使える)公衆無線LANサービス, etc. (But you can use 便利 for these, too)
And 利便性 does sound more formal; it's rarely used in casual conversations.
EDIT:
After the discussion below and Google search, I think 利便性の高い家 and 便利な家 well illustrated the difference of the two words.
Quite contrary to Kentaro Tomono's statement, apparently 利便性の高いマンション almost always refers to its location -- good access to the nearby facilities such as a station, supermarket, school and library.
- 「利便性」とは、(中略)まず第一には駅からの近さや都心などターミナル駅までの所要時間などのことを指します。(from All About マンション購入術)
- 利便性とは交通や買い物などの便利さのことです。 (from 新版 マンションはこうして選びなさい)
It was not until I checked the 57th Google result that I could find this term used for a different aspect of residency.
便利なマンション also refers to the same thing in most cases (e.g. 通勤に便利な家). But it was far easier for me to find different examples, such as 家具付きのマンション, エアコン完備のマンション, あると絶対便利なマンションの施設.